Telephone system employing nonnumerical switches for extending calling lines to numerical switches or to operator-controlled switchboard



June 19, 1951 R. w. JONES 2557,382

TELEPHONE SYSTEM EMPLOYING NONNUMERICAL SWITCHES FOR I EXTENDING CALLING LINEs T0 NUMERICAL SWITCHES OR TO OPERATOR-CONTROLLED SWITCHBOARD Filed Oct. 18, 1947 4 Sheets-Sheet 1 coMMoN TO -w u. UNES IN SERIES THROUGH ALL LINES I VENTOR. ROY WI JCiXJES ATTOR NEY June 19,, 1951 w, JONES 2557,382

TELEPHONE SYSTEM EMPLOYING NONNUMERICAL SWITCHES FOR EXTENDING CALLING LINES T0 NUMERICAL SWITCHES OR TO OPERATOR-CONTROLLED SWITCHBOARD Filed 0612. 18, 1947 4 Sheets-Sheet 2 G0 NNECTO RS Efiiiiiffii Tiifiiffii Ii GROUP OF SOUNE EOUIPMENTS 2 GROUP OF 50 LINE EQUIPMENTS FIG.2

CONNECTORS L 1 L l I GROUP 0* SOLINE EQUIPMENTS 2 GROUP OF 50 LINE EQUIPMENTS mi 6 7 a if? @Wi ft:

9 ?IO J L I I GROUP OF 50 LINE EQUIPMENTS 2 GROUP OF 50 LINE EQUIPMENTS 99 IN V ENTOR.

ROY W. JONES ATTORNEY June 19, 1951 R w JONES 2557,382

TELEPHONE SYSTEM EMPL'oyINc; NONNUMERICAL SWITCHES FOR EXTENDING CALLING LINEs T0 NUMERICAL SWITCHES 0R Filed Oct. 18, 1947 T0 OPERATOR-CONTROLLED SWITCHBOARD 4 Sheets-Sheet 5 TO CONN- TO CONN TO CONN. TO CONN mm TRKS.

ES THROUGH I.--+: I LINES UNES 2- 49 6| T62 63 64 as as 665 CONN NE TERM.

OF 88 66? LINEI I l 627i INVENTOR. ROY W JONES TTORN EY June 19, 1951 J 53 2557,382

R. W. ON TELEPHONE SYSI'EM EMPLOYING NONNUMERICAL SWITCHES FOR EXTENDING CALLING LINES TO NUMERICAL SWITCHES OR TO OPERATOR-CONTROLLED SWITCI-IBOARD '4 Sheets-Shet 4 Filed Oct. 18, 1947 uh'e 100 LINE INVEN TOR. ROY W. JONES ATTORNEY com m en/1 Patented June 19, i951 UNITED STATES PATENT 2,557,382 F FI C E Roy W. Jones, Rochester, N. Y., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application October 18, 1947, Serial No. 780,614

Claims.

The present invention relates in general to automatic and semi-automatic telephone systems, and more particularly to systems employing nonnumerical switches for extending calling lines to numerical switches or to operator-controlled switchboards.

'It is an object of the invention to provide in telephone systems of the characters described, new and novel circuit means for accomplishing the various telephone connections.

Another object of the invention is to provide in telephone systems of the characters described, novel and efficient non-numerical switches which are used as lineswitches for extending outgoing calls from line circuits associated with the lineswitches.

A further object of the invention is to provide in telephone systems of the characters described, non-numerical switches which incorporate trunk connecting means in a new and novel manner for connecting the non-numerical switches to outgoing trunks.

A still further object of the invention is to provide in telephone systems of the characters described, new and novel arrangements whereby the trunks outgoing from two groups of line equipments are graded to form a combination of first-choice trunks individual to each group of line equipments and multiple trunks common to both groups of line equipments as secondary choices.

Another object of the invention is to provide in telephone systems of the characters described, novel circuit means for preventing double connections in a group of non-numerical switches.

Another object of the invention is to provide in telephone systems of the characters described, an improved line circuit arrangement employing a quickto restore line relay and novel circuit means whereby the line relay is permitted to restore immediately the line circuit is connected to a trunk extending therefrom.

A feature of the invention resides in the arrangement wherein connecting means individual to 'a non-numerical switch and common to the trunks serving the switch is operated by the cutolf relay of the switch to connect the switch to one of the said trunks only after an operation of the associated line relay has prepared, or conditioned, the cut-off relay for such action.

Another feature of the invention is the provision in a group of non-numerical switches wherein a chain circuit common to the line relays of the switches is effective to cause the line relays associated with simultaneously calling lines to operate in sequential order, of new and novel circuit means independent of any control by said chain circuit for causing the immediate re- 2 operation of the line relay associated with a calling line which fails to start dialing'within a prescribed time interval after having been extended through its non-numerical switch to a numerical switch, the re-operation of the last mentioned line relay causing its associated non-- numerical switch to be placed in a locked out to the cut-off relays instead of to the line relays,-

contacts on the line relays rendering the chain circuit normally ineffective.

A further feature of the invention relates to the employment of new and novel means for always automatically pre-assigning a trunk which is individual to a group of line circuit equipments, when the trunks outgoing from the group of line circuit equipments are graded, whenever the individual trunk becomes free regardless of whether the" trunk is next in numericalsequence for pre-assignment.

An additional feature of the invention concerns the novel arrangement of connecting means individual to each of the non-numerical switches in a group with respect to the trunks serving thegroup, whereby all of the connecting means are so conditioned by the pre-assignment of any trunk that any one of the switches can thereafter be caused to operate the connecting means in-' dividual to that particular switch for connectingthe switch to the pre-assigned trunk.

There are other objects and features of the invention having to do for the most part with the circuit details necessary to carry out the objects and features above enumerated. The various objects and features of the invention will be understood best from a perusal of the following description of the drawings comprising Figures 1' to 7 inclusive, which show by means of trunking and circuit diagrams a sufiicient amount of apparatus to enable the invention to be described and understood.

Figure 1 shows a plan whereby any number of lines may have access to any number of outgoing trunks.

Figure 2 shows an arrangement whereby line equipments divided into two subgroups of 50 line equipments each and each subgroup having access to 10 outgoing trunks, are provided with 20 percent trunking facilities.

Figure 3 shows an arrangement whereby 100' line equipments are provided with eleven percent trunking facilities by means of graded" trunks. v Figure 4 shows an arrangement whereby 100- line equipments are provided with 15 percent trunking facilities by means of graded trunks.

Figure 5 shows, in simple form, time limit control facilities for timing out and disconnecting an outgoing call whereon dialing is not started within a prescribed time interval after having been extended to a numerical switch.

Figures 6 and 7 taken together show the circuit arrangements of a plan wherein 100 line equipments, divided into two subgroups of 50 line equipments each, are served by graded trunks comprising two individual and nine common trunks.

Referring particularly to Figures 1, 6 and '7, the non-numerical switches, the trunk connecting means, and the common control trunk pre-assigning means are of the mechanical arrangement shown and described in detail in the Patent No. 2,541,354, issued February 13, 1951, to K. W; Graybill, with the general exception that the electromagnet for operating the common control trunk pie-assigning means is equipped with an armature-operated pawl for advancing the common cam shaft upon the energization of the electromagnet, whereas in the structure shown and described in Patent No. 2,541,354 the operation of the electromagnet tensions a spring which drives the common cam shaft upon the de-energization of the electromagnet. The connector switch shown in Figure 1 is of the well-known Strowger switch mechanism type having vertical and rotary movement, although any well-known type of switch may be employed with the present invention. Associated with the mechanical arrangements shown in Figures 1, 6 and '7 are sufficient circuit details for completing the trunking plans involved therein.

The time limit control switch shown in Figure 5 is of the well-known minor step-by-step type, and comprises a single set of bank contacts, a wiper associated with the bank contact set, means comprising a stepping magnet and a ratchet and pawl mechanism (not shown) for driving the wiper over the bank contacts, an off-normal contact spring set which is operated when the wiper is advanced from the first bank contact, and means comprising a release magnet for causing the wiper to be returned to the normal position (first bank contact). It should be understood, however, that the time limit control switch need not be exactly as shown, as any well-known timing device method may be employed.

The relays, resistors and condensers shown in Figures 1, 5, 6 and 7 are typical apparatus units used in telephone systems, and may be of any well-known type.

It should be understood at this time that while a plurality of battery connections are shown in the drawings, they are preferably the same battery. Also, in order to simplify the drawings further, such well-known facilities as busy keys, jacks for enabling an attendant to plug into the various switches, spark quenching apparatus, ringing and tone generating equipment, and the like have been omitted.

Having described the equipment and apparatus, a detailed description of the operation will now be given.

Outgoing trunking operation In the circuit diagram of Figure 1 are shown two lines and two trunks designated line A, line Z, trunk I and trunk l0 respectively. The vertical conductors in the diagram between lines A and Z are broken to indicate that any desired number of lines (dependent upon the grade of service to be rendered) may be interposed between lines A and Z. Similarly, the horizontal conductors between trunks I and 10 are broken to indicate that trunks 2 to 9 may be included. It should be understood, however, that the number of trunks need not be exactly ten but may be more or less according to desire or the amount of traffic offered by the total number of lines. The lines may be equipped with telephone instruments of any well-known manual or automatic type, according to the kind of subscriber service it is intended to provide, or the lines may be connected to suitable equipment on an operator-controlled switchboard to care for service from and to such a manual switchboard. The trunks may terminate in automatic switches of any wellknown type for providing outgoing service from the lines, or the trunks may terminate in an operator-controlled switchboard in order that outgoing calls initiated on the lines may be completed by operators. For the purpose of this explanation it is assumed that the lines are equipped with'telephone instruments of the automatic dial type, and that the trunks terminate in connector switches of the well-known Strowger type.

In addition to the lines and trunks shown in Figure 1, a sufiicient amount of mechanical parts of the invention covered by Patent No. 2,541,354 are included in the diagram to make the explanation more readily understandable, but these mechanical parts are shown in diagrammatic form rather than in elevation in order to reduce Figure 1 to its simplest form. Only general explanation of these mechanical parts and their operations will be given in this specification, as reference may be had to the aforementioned Patent No. 2,541,354 for a complete understanding of the inter-relationship of these mechanical parts and their operations.

Referring now to Figure 1, bare wire conduc-' tors 2 and 3 are supported in a vertical plane and are connected to trunk l, and in a similar manner bare wire conductors 4, 5 and 6 are connected to trunk 10. As in the case of the exact number of trunks, the number of vertical bare Wire conductors connected to each trunk need not be exactly three but may be more or less as the circumstances require. In addition to being connected to trunk I, vertical conductors l, 2 and 3 are connected by means of conductors 56, 5'! and 58 to connector switch I0, and similarly vertical conductors 4, 5 and 6 are connected to connector switch I00. Connectors l9 and I00 may be of any of the Well-known Strowger connector switch designs according to circumstance and, therefore, it is considered satisfactory to include herein only enough of the connector to properly complete this circuit explanation.

Line A is connected to conductors l0! and 92 leading to the resting contacts of armatures E21 and I22 respectively of a line circuit and. also to the horizontally disposed line equipment conductors H and 12. In a similar manner, line Z is connected to another line circuit and to the horizontally disposed line equipment conductors 2i and 22. The connector terminals of line A (over which calls outgoing to line A are completed) are connected to conductors l5, l6 and II leading to line equipment conductors ll, I2 and I3 respectively, and in a similar manner the connector terminals of line Z are connected to conductors 25, 25 and 21 leading to line equipment conductors 2|, 22 and 23 respectively.

Each horizontally disposed line equipment conductor such as I I has a vertically disposed mem-- her depending therefrom for each of trunks I and III. The left-hand vertically disposed depending member II is associated with bare wire conductor I of trunk I, and the right-hand depending member II with bare wire conductor 4 of trunk Ill. In a similar manner there are vertically disposed depending members from conductors I2, I 3, EI, 22 and 23 associated with bare wire conductors of trunks I and ID. The lower, or free, ends of the left-hand vertical members II, I2 and I3 are close to but clear of the related conductors I, 2 and 3 of trunk I, and are arranged for being pressed into electrical contact with conductors I, 2 and 3 thereby to connect line A with trunk I, and in a similar manner the free ends of right-hand vertical members II, I2 and I3 are arranged for being pressed into contact with conductors 4, 5 and '6 thereby to connect line A with trunk I0. The free ends of vertical members 2I, 22 and 23 are also arranged for being pressed into contact with either conductors I, 2 and 3 of trunk I or conductors 4, 5 and 6 of trunk I9 thereby to connect line Z with trunk I or trunk In as the case may be. In Figure 1, the means for connecting vertical members I I, I2 and I3 to the conductors of either trunk I or trunk I6 is represented in simple diagrammatic form by the horizontal plate II9 and its six vertical arms, and in a similar manner the means for connecting vertical members ZI, 22 and 23 to the conductors of either trunk I or trunk I is represented by the horizontal plate I4! and the associated six vertical arms.

When a trunk is in the idle position, no set of vertical depending members associated with that trunk can be pressed into contact with the conductors of that trunk and, consequently, no line circuit having access to that trunk can be connected to the trunk under such conditions. For example, trunk I3 is shown in the idle position, and it will be noted that the lower ends of righthand vertical members II, I2 and I3 are above the horizontal plane of the corresponding top ends of the right-hand vertical arms of plate I I9, and that any subsequent operation of plate IIS to the right would cause the right-hand vertical arms of plate III! to pass underneath the lower ends of right-hand vertical members II, I2 and I3. The depicting of lower ends of right-hand vertical members II, I2 and I3 above the top ends of the corresponding vertical arms of plate H9 is a simple diagrammatic means for indicating that the right-hand vertical members II, I2 and I3 are not in a condition for being pressed into contact with conductors 4, and 6 of trunk Ill and are, therefore, unafiected by any subsequent operation of plate H9. The lower ends of right-hand vertical members 2 I, 22 and 23 are shown above the horizontal plane of the corresponding top ends of the right-hand vertical arms of plate I47 to similarly indicate that righthand vertical members 2|, 22 and 23 are also not in a condition for being pressed into contact with conductors 4, 5, and 6 of trunk II]. It is, therefore, apparent that neither line A or line Z can be connected to trunk III while trunk II) remains in the idle position.

In order that any one of the sets of vertical depending members associated with a trunk which is in the idle position may be connected to the conductors of that trunk, the sets of vertical members associated therewith are so conditioned that an operation of either horizontal plate I I3 or horizontal plate I41 to the right will be effective to press one of the sets of vertical members into contact with the conductors of the trunk. The manner in which the conditioning of the sets of vertical members associated with a trunk in the idle position is accomplished is described in the following three paragraphs.

Associated with each trunk is a vertically disposed bar, such as bar 34 with trunk I and bar 44 with trunk II]. These bars are for the purpose of causing the conditioning of the vertical members associated with the conductors of the related trunks in order that lines subsequently initiating outgoing calls may be connected to the trunks. The operation of conditioning the vertical members associated with the conductors of a trunk is known as pre-assigning the particular trunk (which was in the idle position just prior to the conditioning operation) for subsequent use on an outgoing call initiated by one of the lines having access to the trunk. The arrangement of the bars with respect to the trunks, and the relationship of the bars with each other, are such that only one bar at a time can pro-assign a trunk. As soon as a pre-assigned trunk is taken into use, common control equipment immediately causes another trunk in the idle position to be pre-assigned, and successive pro-assignments of trunks in the idle positions will occur as addi tional outgoing calls are initiated on the lines.

The vertically disposed bars, such as 34 and 44, have upwardly and downwardly movements controlled by carn-operated levers upon which the lower ends of the bars rest. Bar 44 associated with trunk It) is shown in the upward, or normal, position and while in this position cannot cause the conditioning of right-hand vertical members II, I2 and I3 and right-hand vertical members 2|, 22 and 23. The right-hand vertical members II, I2 and. I3 are, therefore, unafiected by any subsequent operation of plate I I9, and righthand vertical members 2|, 22 and 23 correspondingly unaITected by any subsequent operation of plate I41. Trunk III, consequently, remains in the idle position for the time being. The dotted line 41 projecting from bar 44 across right-hand vertical members I I, I2 and I3, and the dotted. line 48 projecting from bar 44 across right-hand vertical members 2I, 22 and 23 indicate that bar 44 controls the conditioning of these particular vertical members.

Bar 34 associated with trunk I is shown in the lower, or operated, position, and in this position has pre-assigned trunk I. Before bar 34 was dropped to the lower position by the operation of lever 32, trunk I was in the idle position, and the purpose of dropping bar 34 to the lower position is to cause bar 34 to pre-assign trunk I for use on a subsequent outgoing call from either line A or line Z by having bar 34 cause the conditioning of left-hand vertical members II, I2 and I3 and left-hand vertical members 2!, 22 and 23. The dropping of bar 34 accomplishes the conditioning of left-hand vertical members II, I2 and I3 and left-hand vertical members 2I, 22 and 23 by permitting these vertical members to drop by gravity to corresponding lower positions whereby the lower ends of these vertical members are below the horizontal planes of the top ends of the left-hand vertical arms of plate H9 or plate I41. It is, therefore, apparent that any subsequent movement of plate H9 to the right will cause its left-hand vertical arms to press left-hand vertical members II, I2 and I3 into electrical contact with conductors I, 2 and 3 of trunk I, and thatany subsequent movement of plate I41 to the right will cause its left-hand vertical arms to press left-hand vertical members 2I, 22 and 23 into electrical contact with conductors I, 2 and 3 of trunk I. The depicting of the lower ends of left-hand vertical members II, I2 and I3 and the lower ends of left-hand vertical members 2|, 22 and 23 below the horizontal planes of the top ends of the respective left-hand'vertical arms of plates H9 and I41 is a simple diagrammatic means for indicating that left-hand vertical members II,' I2, I3, 2|, 22 and 23 have been conditioned for being pressed into contact with conductors I, 2 and 3 of trunk I. The dotted line 31 projecting from bar 34 across left-hand vertical members I I, I2, I3, and the dotted line 38 projecting from bar 34 across left-hand vertical members 2I, 22 and 23 indicate that bar 34 controls the conditioning of these particular vertical members. For detail information concerning the precise arrangement of the mechanical parts involved in the condi tioning of vertical members II, I2, I3, 21, 22 and 23 and the exact operation of such mechanical parts, reference should be had to the previously mentioned application.

Considering now that an outgoing call is initiated on line A and that trunk I has been pre-assigned as shown in Figure 1, the circuit of line relay H is completed from ground, upper winding of relay IIO, armature I2I, conductor IIlI, direct-current loop (not shown) of line A, conductor I02, armature I22, lower winding of relay IIO, armatures II I, I36, II5, conductor I05, armature I06, resistor I 01 to battery, causing relay I II! to first operate its X contact associated with armature II3. The operation of this X contact switches the lower winding of relay IIO directly to conductor I05 independent of the resting contacts of armatures II4, I33 and H5. Relay IIO then operates completely. At armature I I5, relay I I0 opens the chain circuit to resistor I01 thereby to prevent the completion of the circuit through the lower winding of the line relay as sociated with line Z should an outgoing call be initiated on line Z. At armature IIB, relay IIO completes a circuit to common relay I35 by way of armature I3I and resting contact, causing relay I35 to operate and open a further point in the previously mentioned chain circuit to the lower winding of the line relay of line Z at armature I36. By means of armature II1, relay H0 inserts trigger device I I8 between the lower arm of cut-off relay armature I 26 and the left-hand end of horizontal plate II9. At armature III and working contact, relay I I0 extends ground to the C connector terminal of line A by way of conductors I03, I3 and I1 to guard line A against intrusion.

At armature I31, common relay I35 connects ground potential to conductor I of pre-assigned trunk I by way of armature 8 and working contact, thereby seizing trunk I and the associated connector I0. It should be understood at this time that relay 1 of trunk I was operated over the circuit completed at contact 35 at the time trunk I was pre-assigned and is held operated during tery, causing cut-off relay I to operate. At armature I 24, cut-off relay I20 connects its winding to ground by way of armature III; and, at armature I25, completes the circuit to lockout relay I by way of armature III, causing lockout relay I 30 to operate. The operation of cut-on relay I20 also causes armature I26 to move horizontal plate I I9 to the right because the presence of trigger device II8 between the lower arm of armature I26 and the left-hand end of plate IIS provides the addition necessary to the lower arm of armature I26 to cause the movement of plate IIB to the right. Without the aid of trigger device II8, the lower arm of armature I26 in its operated position would just reach the left-hand end of plate II9 but could not cause the moving of plate II9 to the right. The right-wise movement of plate II9 causes its left-hand vertical arms to press left-hand vertical members II, I2 and I3 into contact with conductors I, 2 and 3 of trunk I. The right-hand vertical arms of plate I I9 pass underneath the lower ends of right-hand vertical members II, I2 and I3 and, therefore, no connection can be extended from line A to trunk I0 at this time. The vertical arms of plate I I9 are shown as heavy filled-in lines to indicate that plate H9 is electrically insulated from vertical members II, I2 and I3.

The pressing of left-hand vertical members II and I2 into contact with conductors I and 2 of trunk I extends line A to the operating circuits of connector I0 thereby transferring the control of relay 50 to the direct-current loop of line A. As a result of this transference of control, ground potential will remain on trunk conductor 3 as long as line A retains control of connector I0. When lockout relay I30 was operated by the action of cut-off relay I20, it opened the circuit to common relay I at armature I3I, and the restoration of common relay I35 opened one circuit to the upper winding of relay at armature I31. The slow release action of relay 55, however, retains ground potential on trunk conductor 3 until relay 50 is operated over the loop of line A.

The pressing of left-hand vertical member I3 into contact with conductor 3 of trunk I extends the ground potential on conductor 3 to the winding of cut-off relay I20 by way of armature I24 thereby locking cut-off relay I20 in the operated position independent of the ground from armature III of line relay H0. The operation and locking of cut-oil relay I20 disconnects the windings of line relay I I0 from conductors IOI and I02 and from line A, thereby clearing line A of attachments. The restoration of common relay I35 also completes a circuit in multiple to relay 20 and electromagnet 30 by way of ground on conductor 3, armature 9 and armature I38 for the purpose'of causing the pre-assignment of another idle trunk in the manner to be described later in this section.

The disconnection of the windings of line relay I ID from line A by the operation of armatures I2I and I22 causes line relay I I0 to restore to normal position. Since the ground on conductcr 3 of trunk I is extended to the winding of cut-oil relay I20 immediately the left-hand vertical member I3 is pressed into contact with conductor 3 by the operation of cut-off relay I20, it is unnecessary [or line relay I I0 to be of the slow-to-release type for the purpose of retaining ground on the winding of cut-off relay I20 for a short period after cut-off relay I20 has disconnected line relay IIO from conductors IOI and I02 and, therefore, line relay H0 is shown as a fast releasing relay. At arma-- 9 ture II5, relay II9 completes th chain circuit for the lower winding of the line relay associated with line Z in order that this line relay may operate should line Z now initiate an outgoing call. At armature H4, line relay II9 completes the chain circuit to its own lower winding. The restoration of line relay I I9 does not remove trigger device IIB from its position between the lower arm of armature I29 and the left-hand end of plate H9, as armature I29 firmly holds trigger device II8 against the left-hand end of plate I I9, thereby causing plate II9 to retain left-hand vertical members II, I2 and I3 in contact with conductors I, 2 and 3 of trunk I.

Digressing for the moment from th description of the call from line A, an explanation will now be given of the method of automatically pro-assigning trunks to successive-calls initiated at the local stations such as A and In the foregoing description it was stated that cam-operated levers controlled the upwardly and downwardly movements of the vertically disposed bars, such as bars 34 and 44, associated with the trunks. Lever 32 is controlled by cam 3I, and lever 42 by cam 4|. Cams 3I and M are mounted on a common shaft 29 which is operative by electromagnet 39 through the medium of armature pawl 39. Lever 32 is pivoted at 33 and, consequently, when the lefthand end of lever 32 permitted bar 34 to drop by gravity to its lower position, the right-hand end of lever 32 caused contact 35 to complete an obvious circuit to relay I of trunk I. The dropping of bar 34 caused the pre-assignment of trunk I, and the initiation of the call on line A caused line A to be extended over trunk I to connector In in the manner previously explained.

As previously stated, th restoration of common relay I35 completes a circuit in multiple to relay 29 and electromagnet 39 and, as a consequence, both relay 29 and electromagnet 39 operate. At armature I 9, relay 29 opens the circuit to conductor I99 of the line equipment of line Z thereby to prevent the operation of the cut-off relay of line Z line equipment so that line Z cannot be extended to trunk I should line Z initiate a call at this time. The operation of electromagnet 39 causes armature pawl 39 to advance shaft 29 one trunk step in a clockwise direction. Cam 3I, therefore, leaves the right-hand end of lever 32, and the tensioned springs associated with contact 35 cause lever 32 to raise bar 34 to the upper position. Contact 35 is also opened by this movement of lever 32, causing relay I associated with trunk I to restore and open the multiple circuit to relay 29 and electromagnet 39 at armature 9. Electromagnet 39 restores immediately but relay 29 is of the slow-to-release type. Pawl 49 retains shaft 29 in the advanced position. The raising of bar 34 has no eifect on the established connection of line A with connector I 9, as cut-ofi relay I29 continues to hold plate II 9 to the right thereby maintaining left-hand vertical members II, I2 and I3 in firm contact with conductors I, 2 and 3 of trunk I. The raising of bar 34, however, causes left-hand vertical members 2|, 22 and 23 to be returned to their original, or normal, positions in which positions the lower ends of thesevertical members are above the horizontal plane of the top ends of the lefthand vertical arms of plate I41 and, therefore, no subsequent movement of plate I4? to the right can cause the extension of line Z to conductors I, 2 and 3 of occupied trunk I. v

.As the operation of armature pawl 39 stepped 9am, 31. away from lever 32, it also caused cam M to approach and operate the right-hand end of lever 42 associated with trunk I9, thereby causing contact 45 to complete an obvious circuit to relay I8 of trunk I9. Assuming now that trunk I9 is in the idle position, then the lefthand end of lever 42 causes bar 44 to drop by gravity to its lower position, thereby pro-assigning trunk I9 in a manner similar to that previously described in connection with the pre-assignment of trunk I. If, however, trunk I9 is cocupied at the time relay I8 operates, the multiple circuit to relay 29 and electromagnet 39 will be completed from ground on conductor 6 of trunk i 9, armature 28 and armature I38, causing electrcmagnet S9 to operate and retaining relay 29 in the operated position. Relay 29 is slow to release and, therefore, did not restore when its circuit was opened at armature 9 before its circuit is completed at armature '28. The function of relay 29 is to maintain the multiple operating circuit to the cut-off relays of the lines open while an idle trunk is being found and preassigned, in order that no calling line will be extended to an occupied trunk.

The re=operation of electromagnet 39 due to trunk I9 being found" in the busy condition causes armature pawl 39 to advance shaft 29 another trunk step which in the normal event would select trunk 9 (not shown). Occupied trunk I9 is thus by-passed, and relay I9 restored to normal. If trunk 9 is in the idle position, then there will be no ground potential returned to armature I38 from trunk 9, and trunk 9 is then pro-assigned in readiness for the next outgoing call on a line circuit. In the manner just described, occupied trunks are by-passed and trunks in the idle position are preassigned.

Returning now to the connection of line A with connector I9 by way of trunk I, as previously stated the ground on trunk conductor 3 from relay 55 of connector I9 is extended through lefthand vertical member I3 to the winding of cutoff relay I29 and to conductor I'I leading to the C terminal of the connector bank terminals of line A. The ground on the winding of cut-off relay I29 causes cut-off relay 129 to maintain the connection of line A with connector I9 as long as the direct-current loop of line A remains in tact. The ground to the C terminal of the con-=- nector terminals of line A guards line A from intrusion by other calls as is conventional in telephone systems of this character.

- Assuming further that line A desires a con nection with line Z, then line A controls connector I9 in a well-known manner to cause wipers 5!, 52 and 53 of connector I9 to connect with the bank terminals of line Z. Connector I9 tests the C bank terminal of line Z for a possible busy condition and finding line Z in the idle position then connects ground potential to the winding of cut-oif relay I49 by way of conductors '21, 23, I99, armature I39 and resting contact, conductor I43, winding of cut-off relay I49 to battery. Cut-off relay I49 operates overthe circuit just traced and locks to the ground from wiper 53 by way of armature I44. The ground on wiper 53 also guards line Z from intrusion by other calls. MIJ'clears line Z of attachments; and, at arma ture #45, completes the circuit to the associated lockout relay. The operation of cut-off relay I49 also causes armature armature I46 cannot cause a movement of plate 4? to the right because the lower arm of arma ture 49 in the operated position just reaches the At armatures MI and I42, cut-01f relay I46 to operate but.

am e

A from the windings of relay 50 of connector I0,

and to line Z from the windings of relay 50.

Upon the termination of the conversation and the opening of the direct-current loop of line A, connector I is restored to normal in a wellknown manner. The consequent removal of ground potential from conductor 3 of trunk I opens the locking circuit of cut-oil relay I20, and cut-ofi relay I20 restores. At armatures I2I and I22, cut-ofi relay I20 reoonnects the windings of line relay IIO across the conductors of line A: at armature I25, opens the circuit to lockout relay I30, causing lockout relay I30 to restore; and the release of armature I26 permits trigger device II8 to drop to its normal lower position and also permits plate I I9 to move to the left under the power of tensioned spring I21. The restoring of plates II9 causes the disconnection of left-hand vertical members II, I2 and I3 from trunk conductors I, 2 and 3, and the disconnected left-hand vertical members II, I2 and I3 are then restored to their original, or normal, positions in the manner described in the previously mentioned application, in order that their lower ends may be raised above the horizontal plane of the top ends of the left-hand vertical arms of plate H9. The disconnection of wiper 53 of connector I0 opens the locking circuit of cut-oil relay I40 thereby permitting cutofi relay I40 to restore to normal. At armatures MI and I42, cut-ofi relay I40 reconnects the windings of the associated line relay across the conductors of line Z; and, at armature I45, opens the circuit to the associated lockout relay. Trunk I is now in the idle position.

It will now be assumed that lines A and Z are in their normal idle positions, that trunk I has been pre-assigned as indicated in Figure 1, that connector I0 has been fitted with the time limit control facilities shown in Figure for automatically removing the ground potential from trunk conductor 3 should a calling line fail to dial within a definite time interval after having seized connector I0, and that line A has initiated an outgoing call. Under these assumed conditions line relay IIO operates and causes cut-off relay I to extend line A to connector I0 by way of trunk I in the manner previously described. It is further assumed that line A after having initiated the outgoing call fails to dial the wanted number before the expiration of the definite time interval and, as a consequence of this failure to dial within the definite time interval, the ground potential on trunk conductor 3 is removed. Cut-off relay I20, therefore, restores and opens the circuit to lockout relay I30 at armature I but lockout relay I is of the slow-to-release type and remains operated for a short interval. In the meantime the windings of line relay I I0 are reconnected across the conductors of line A at armatures I2I and I22, and since the direct-ourrent loop of line A remains closed, line relay IIO immediately re-operates and completes a locking circuit to lockout relay I30 by way of armature H5 and armature I3I and working contact before lockout relay I30 has had time to restore. When cut-01f relay I20 reconnected the windings of line relay IIO to line A, line relay H0 was able to operate immediately, regardless of 12 whether another line relay had previously operated on an outgoing call and was holding the chain circuit to line relay IIO open, because the battery end of the lower winding of line relay I I0 was connected direct to battery through resistor.

I01 at armature I33 independent of the chain circuit through armatures II4, I35, H5 and I08. The restoration of cut-off relay I20 also releases trunk I and connector I0 in the manner previously explained, thereby restoring trunk I to the normal idle position. Line A is now in the locked out position with line relay I I0 and lockout relay I30 both operated. At armature I32, lockout relay I30 maintains the operating circuit to the winding of cut-off relay I20 open so that cut-oi! relay I20 cannot re-operate as long as the closedloop condition on line A continues to exist. When line A disconnects, line relay III! restores and opens the locking circuit to lockout relay I30 at armature IIO, thus permitting lockout relay I30 to restoreand re-establish the cut-off relay operating circuit at armature I32 and resting contact.

The time limit control facilities shown in Figure 5 and associated with connector I0 consists of relays I0 and 85, time limit control switch 59 and associated stepping magnet 00 and release magnet 95, and additional contacts to relays 50 and 55 of connector I0. The first six bank contacts of time limit control switch 59 are shown multipled together, the seventh bank contact thereby forming a definite predetermined off-normal position. It should be understood, however, that the arrangement of the time limit control switch need not be exactly as shown, as any well-known timing device method may be employed. The operation of the time limit control equipment is as follows:

When connector I0 is seized in the manner previously described, relay 50 completes an obvious circuit to relay 55 which in turn connects ground potential to trunk conductor 3 by way of conductor 58 (Figure 5), wiper of time limit control switch 59, bank contact I, contact multiple and conductor 60. This ground potential over trunk conductor 3 causes cut-ofi relay I20 to operate in the manner also previously described. The operation of relay 55 also causes relay 10 to operate over the circuit by way of conductor 61. At armature 82, relay I0 connects ground potential to the winding of stepping magnet by way of armature 81 and resting contact. The other end of the winding of stepping magnet 90 is connected to common contact 9| which is operated at certain intervals by means of the common timer cam 99 and, therefore, stepping magnet 90 is energized and advances the wiper of time limit control switch 59 one bank contact step for each revolution of timer cam 90. The timer cam 99 may, for example, be arranged to make one revolution every five seconds, with the result that the wiper will be brought into engagement with bank contact 7 after a period of 30 seconds, or one-half minute, has lapsed. The timed interval need not be limited to one-half minute as the timer cam 99 can be operated at any desired speed, and any number of bank contacts can be multipled together to obtain the desired overall timed interval.

Should line A fail to start dialing before the predetermined time interval has lapsed, the wiper of time limit control switch 59 will pass from bank contact 6 to bank contact I. Ground potential is, therefore, removed from conductor 50, and cutoff relay I20 restores as previously explained.

Should line A, however, commence dialing before the predetermined time interval has lapsed, i. e.,

before the wiper of time limit control switch 59 leaves bank contact 6, relay 85 is operated from ground by way of conductor 69 and armature 8|. Relay 85 looks to ground on conductor 58 by way of armature 86. At armature 8?, relay 85 removes ground from the winding of stepping magnet 90 to prevent further rotation of the wiper of time limit control switch 59 and, at armature 88, completes the circuit to release magnet 95. Release magnet 95 causes the wiper to be returned to the normal position (bank contact I) in a well-known manner, and the opening of offnormal spring set 9 3 as the wiper reaches the position of bank contact I disables the operating circuit of release magnet 95. Line A, therefore, remains connected to trunk l and connector I0.

Outgoing trunking Operation with graded trunks In Figure 1 are shown a number of lines having access to a number of outgoing trunks. Theoretically, as indicated in the preceding section of this specification, the maximum number of line equipments which may be mounted on a single framework or rack may be any number according to particular requirements or preference, as may also be the maximum number of trunk outlets. There are, however, usually limitation of a mechanical nature, such as overall space dimensional restrictions, shipping conditions and the like, which make it undesirable or uneconomical to provide for more than a certain maximum number of line equipments and trunk outlets on a single framework. For example, conditions may make it necessary to limit the number of line equipments to 100, and the trunk outlets accessible to the 100 line equipments to 10. The outgoing trunks terminating the trunk outlets in such an instance would, therefore, provide for a maximum of 10 percent trunking. Should it be desirable or necessary to provide for a greater percent of outgoing trunking for the 100 line equipments than 10, and it is unfeasible to increase the one group of trunk outlets beyond 10, then the 100 line equipments may be divided into two subgroups of 50 line equipments each, with each subgroup of 50 line equipments having access to 10 trunk outlets. If each group of 10 trunk outlets is then connected to 10 outgoing trunks, the percent of outgoing trunking thus provided is increased to percent. A lesser number of outgoing trunks connected to each group of 10 trunk outlets would correspondingly reduce the outgoing trunking below 20 percent.

Figure 2 shows in simple diagrammatic form two subgroups of 50 line equipments, each subgroup having 10 trunk outlets represented by the small circles designated I to ID inclusive. Connected to the 10 trunk outlets of the left-hand subgroup are 10 connectors (outgoing trunks) represented by the squares designated I to II) inclusive, and correspondingly the 10 trunk outlets of the right-hand sub group are connected to connectors II to 20 inclusive. It is obvious that each subgroup of 50 line equipments is provided with 20 percent outgoing trunking facilities, and

that each subgroup is independent of the other subgroup.

Figure 3 shows an arrangement of two subgroups of 56 line equipments served by 1.1 outgoing trunks, thereby providing 11 percent trunking for the 100 line equipments. The 11 percent of trunking is accomplished by applying.the.w.el1.

known principles of trunk grading whereby trunk I is a first-choice trunk individual to the left-hand subgroup, trunk I I a first-choice trunk individual to the righthand subgroup, and trunks 2 to IE inclusive second-choice trunks common to both subgroups. In a similar manner Figure 4 shows an arrangement whereby the two subgroups are served by 15 outgoing trunks, thereby providing 15 percent trunking for the line equipments. In this arrangement, trunks I to 5 inclusive are first-choice trunks individual to the left-hand subgroup, trunks II to I5 inclusive first-choice trunks individual to the right-hand subgroup, and trunks E to I0 inclusive secondchoice trunks common to both subgroups.

It should be understood that in the short description of outgoing trunking in the preceding three paragraphs the number of line equipments, trunk outlets, and trunks specified are for explanatory purposes only and should not be construed as being binding or restrictive in any manner.

The following explanation of the circuit diagrams of Figures 6 and 7 covers outgoing trunking operation when the trunks are graded in accordance with the arrangement shown in Figure 3.

In the circuit diagram of Figure 6 are shown two lines and ten trunks designated line I, line 50, trunk I, trunks 2 to 9 inclusive, and trunk ID. The vertical conductors between lines I and 5c are broken to indicate that in reality lines 2 to 49 inclusive are interposed between lines I and 50 although not shown. It should be understood, however, that the number of lines need not be exactly 50 but may be more or less according to desire or the grade of service to be rendered. As in the case of Figure l, the lines may be equipped with telephone instruments of any well-known manual or automatic type, according to the kind of subscriber service it is intended to provide, or the lines may be connected to suitable equipment on an operator controlled switchboard to care for service from and to such a manual switchboard. The horizontal conductors broken between trunks I and Ii] are broken toindicate that trunks 2 to 9 inclusive are interposed between trunks I and I6. Trunks 2 to 9 inclusive, however, are not shown in detail. It should also be understood at this time that the number of trunks need not be exactly 16 but may be more or less according to desire or the amount of trafiic offered by the total number of lines. As in the case of Figure l, the trunks may terminate in automatic switches of any well-knowntype for providing outgoing service from the lines, or the trunks may terminate on an operator-controlled switchboard in order that outgoing calls initiated on the lines may be completed by operators. For the purpose of this explanation it is assumed that the lines of Figure 6 are equipped with telephone instruments of the automatic dial type, and that the trunks terminate in connector switches of the well-known Strowger type although the connectors are not shown.

Figure 7 circuit diagram is similar to the circuit diagram of Figure 6 and includes two lines designated line 5! and IN? respectively, a trunk designated trunk II, and multiple appearances of trunk 2- to is inclusive from Figure 6. The vertical conductors between lines 5! and It!!! are broken to indicate that lines 52 to 99 inclusive- 1 trunk II and the multiple appearance of trunk are broken to indicate that multiple appearances of trunks 2 to 9 inclusive are interposed between trunk H and the multiple appearance of trunk ID. The multiple appearance of trunks 2 to 9 inclusive, however, are not shown in detail. As in the case of Figure 6, it is assumed that the lines are equipped with telephone instruments of the automatic dial type, and that trunk I l terminates in a connector switch of the well-known Strowger type.

In addition to the lines and trunks shown in Figures 6 and 7, a suilicient amount of mechanical parts of the invention covered by Patent No. 2,541,354 are included in these two diagrams to make the explanation more readily understandable, but these mechanical parts are shown in diagrammatic form rather than in elevation in order to reduce Figures 6 and '1 to their simplest forma. Only a general explanation of these mechanical parts and their operations will be given in the specification as reference may be had to the aforementioned Patent No. 2,541,354 for a complete understanding of the inter-relationship of these mechanical parts and their operations.

Referring particularly to Figure 6, bare wire conductors 6!, 62 and 63 of trunk l are supported in a vertical plane and are connected to a connector switch (connector switch not shown but would be similar to connector switch ID in Figure 1). Similarly, bare wire conductors 64, 65 and 66 of trunk [0 are connected to a connector switch as are also the bare wire conductors of trunks 2 to 9 inclusive. As in the case of the exact number of trunks, the number of vertical bare wire conductors of each trunk need not be exactly three but may be more or less according to circumstance.

Line I is connected to conductors 601 and 602 leading to the resting contacts of armatures 62l and 622 respectively of a line circuit and also to the horizontally disposed line equipment conductors Gill and 662. In a similar manner, line 50 is connected to another line circuit and to the horizontally disposed line equipment conductors 6H and 612. The connector terminals of line I are connected to conductors 665, 666 and 661 leading to line equipment conductors 66 I, 662 and 663 respectively, and in a similar manner the connector terminals of line 59 are connected to conductors 615, 616 and 611 leading to line equipment conductors 611, 612 and 613 respectively.

The horizontally disposed line equipment conductors 66!, 662, 663, 611, 612 and 613 each have a vertically disposed member depending therefrom for each of the trunks. These vertically disposed vertical members are associated with the conductors of the trunks in order that lines I and 50 may be connected with the trunks in a manner similar to that previously described in this specification for the horizontally disposed line equipment conductors ll, [2, I3, 24, 22 and 23 shown in Figure 1. In Figure 6, the means for connecting vertical members 66!, 662 and 663 to the conductors of the trunks is represented by the horizontal plate (H9 and its vertical arms, and similarly the means for connecting vertical members 611, 612 and 613 to the conductors of the trunks is represented by the horizontal plate 651 and the associated vertical arms.

Trunk 10 (Figure 6) if shown in the idle position, and it will be noted that the lower ends of right-hand vertical members 66l, 662 and 663 are shown above the horizontal plane of the corresponding top ends of the right-hand vertical arms of plate 619, and that any subsequent 7 operation of plate M9 to the right would cause the right-hand vertical arms of plate H9 to pass underneath the lower ends of right-hand vertical members 661, 662 and 663. The lower ends of right-hand vertical members 61!, 612 and 613 are shown above the horizontal plane of the corresponding top ends of the right-hand vertical arms of plate 651 to similarly indicate that righthand vertical members 61!, 612 and 613 are also not in a condition for being pressed into contact with conductors 64, 65 and 66 of trunk [0. It is, therefore, apparent that neither line I nor line 50 can be connected to trunk l0 while trunk [0 remains in the idle position.

In order that any one of the sets of vertical depending members associated with a trunk which is in the idle position may be connected to the conductors of that trunk, the sets of vertical members associated therewith are conditioned in a manner similar to that described in the preceding section so that an operation of either horizontal plate H9 or horizontal plate 651 to the right will be eifective to press one of the sets of vertical members into contact with the conductors of the trunk. Vertically disposed bar 634 is associated with trunk l, and bar 644 with trunk 10 for the purpose of causing the conditioning of the vertical members associated with the conductors of the related trunks in order that lines subsequently initiating outgoing calls may be connected to the trunks. The operation of conditioning the vertical members associated with the conductors of a trunk is known as pro-assigning the particular trunk (which was in the idle position just prior to the conditioning operation) for subsequent use on an outgoing call initiated by one of the lines having access to the trunk. The arrangement of the bars with respect to the trunks, and the relationship of the bars with each other, are such that only one bar at a time can pre-assign a trunk. As soon as a pre-assigned trunk is taken into use, common control equipment immediately causes another trunk in the idle position to be pre-assigned, and successive pre-assignments of trunks in the idle positions will occur as additional outgoing calls are initiated on the lines.

Bar 644 associated with trunk I0 is shown in the normal, or upward, position, and while in this position cannot cause the conditioning of right-hand vertical members 661, 662 and 663 and right-hand vertical members SH, 612 and 613. The right-hand vertical members 66!, 662 and 663 are, therefore, unaffected by any subsequent operation of plate 619, and right-hand vertical members 61l, 612 and 613 are correspondingly unaffected by any subsequent operation of plate 651. Trunk l0, consequently, remains in the idle position for the time being. The dotted line 641 projecting from bar 644 across righthand vertical members SH, 662 and 663, and the dotted line 648 projecting from bar 644 across right-hand vertical members 61!, 612 and 613 indicate that bar 644 controls the conditioning of these particular vertical members.

Bar 634 associated with trunk l is shown in the operated, or lower, position, and in this position has pre-assigned trunk I. When bar 634 was dropped to the lower position, it accomplished the conditioning of left-hand vertical members 66!, 662 and 663 and left-hand vertical members 61l, 612 and 613 by permitting these vertical members to drop by gravity to correof these vertical members are below the horizontal planes of the top ends of the left-hand vertical arms of plate 6I9 or plate 651. It is, therefore, apparent that any subsequent movement of plate 6E9 to the right will cause its left-hand vertical arms to press left-hand vertical members 66E, 6512 and 653 into electrical contact with conductors Si, 62 and 63 of trunk I, and that any subsequent movement of plate 651 to the right will cause its left-hand vertical arms to press left-hand vertical members Bl l, 612 and 673 into electrical contact with conductors BI, 62 and 63 of trunk I. The dotted line 649 projecting from bar 634 across left-hand vertical members 66L 562 and 663, and the dotted line 610 projecting from bar 634 across left-hand vertical members till, 612 and Bit indicate that bar 634 controls the conditioning of these particular vertical members.

Referring now to Figure 7, bare wire conductors H, 12 and 73 of trunk I! are supported in a vertical plane and are connected to a connector switch (not shown). Bare wire conductors l -l, l and 16 of trunk it are supported in a vertical plane but are not directly connected to a connector switch as in the case of conductors H, 12 and 13 but are connected by means of conductors 17, 18 and 19 in cable 86 to conductors 64, 65 and 66 of trunk H3 in Figure 6 thereby multiplying trunk IU of Figure 7 to trunk II] of Figure 6. In similar manner, the bare wire vertical conductors of trunks 2 to 9 inclusive of Figure '7 are multiplied to the vertical conductors of trunks 2 to 9 inclusive of Figure 6. Lines 5| and I90 (Figures 7) are each connected to a line circuit and to the horizontally disposed line equipment conductors TM, 162, TH and H2 respectively in a similar manner to line I of Figure 6. The connector terminals of line 5| are connected to conductors 785, its and 76! leading to line equipment conductors 16], 162. and l63 respectively, and the connector terminals of line 100 to conductors H5, H6 and TH leading to line equipment conductors TH, H2 and 113 respectively. In addition, conductors 604, 635 and 606 are required between the line circuits of Figures 6 and 7 in order that the chain circuit to resistor 609 may be carried through all of the line circuits of Figures 6 and 7 in series for the purpose of preventing more than one outgoing call being extended to a trunk at one time.

The general arrangement of the horizontally disposed line equipment conductors 'IBI, E62, 163, TH, 112 and H3 and the vertically disposed bars 134 and 144 is similar. to that previously described for conductors 66!, 662, 883, (ill, 612 and 613 and bars 634 and 644. It is, therefore, considered unnecessary to include such details here. Bar 144 is associated with trunk iii and is shown in the normal position. Trunk I9 (Figure 7), consequently, is in the idle position. Bar 134 is associated with trunk i I and is shown in the operated position. Trunk Ii, consequently, is in the pre-assigned position.

Considering now that an outgoing call is initiated on line i and that trunk I has been preassigned as shown in Figure 6, the circuit of line relay Bill is completed from ground, armature 62!, conductor 5M, direct-current loop (not shown) of line I, conductor SE32, armature 622, winding of line relay 6 i 6 to battery, causing relay 610 to operate. At armature BiZ, relay Slfl removes the shunt across armature B23 and associated resting contact, thereby permitting the con 18 trol of the chain circuit through all of the line circuits of Figure 6 and Figure 7 to be taken over by armature 823 of the associated cut-off relay. By means of armature fill, relay 6H1 inserts trigger device file between the lower arm of cut-01f relay armature 526 and the left-hand end of horizontal plate 6E9. An armature 6i3, relay BIB extends ground to the C connector terminal of line I by way of conductors 5233, $63, and 661 to guard line I against intrusion. At armature 613, relay Bill also completes a circuit to cut-off relay 629 from ground, armatures EH6, M3, conductor 603,-winding of'cut-off relay 620, armature 6H and working contact, armature 62 i and resting contact, conductor GM to Figure '7, armature (shunted by armature 7B6), conductor it'll, armature Hi8 (shunted by armature 1G9), conductor 606 to Figure 6, armature 653 (shunted by armature 6M), conductor 6. armature 623, resistor 669 to battery, causing cut-off relay 628 to operate.

At armatures- 62| and 622, cut-off relay-62B disconnects line relay 6H] from the direct-ourrent loop of line i but line relay 6! i1 is of the slow-to-release type and, therefore, remains operated for a short period of time. At armature 624 and working contact, cut-01f relay 626 switches its winding to resistor see independent of the chain circuit through the other line circuits. The operation of cut-oil" relay 626 also causes armature 62b to move horizontal plate 689 to the right because the presence of trigger device 6l8 between the lower arm or armature 626 and the left-hand end of plate 685 provides the addition necessary to the lower arm of armature 626 to cause the movement of plate em to the right. The right-wise movement of plate 619 causes its left-hand vertical arms to press lefthand vertical members it I, 862 and 663 into contact with conductors 6i, $32 and 63 of trunk l. The right-hand vertical arms of plate 6H9 pass underneath the lower ends of right-hand vertical members SM, 662 and i563 and, therefore, no connection can be extended from line i to trunk II] at this time. The lower ends of the vertical members (not shown) which are associated with trunks 2 to 9 inclusive (partly shown) would also be above the horizontal plane of the related vertical arms (not shown) of plate GIS and, therefore, no connection can be extended from line I to trunks 2, 3, l, 5, 6, l, 8 or 9 at this time.

The pressing of left-hand vertical members Bill and 662 into contact with conductors BI and 62 of trunk l extends line i to the operating circuit of the connector (not shown) associated with trunk I. The direct-current loop of line I bridged across the and conductors of the connector (not shown) causes a relay (not shown) in the connector to operate in a well-known manner and cause ground potential to be connected to conductor $3 of trunk i. The'pressing of left-hand vertical member 653 into contact with conductor 63 of trunk i extends the ground potential on conductor E3 to the winding of cutoff relay 628, thereby locking cut-off relay $23 in the operated position independent of the ground from armature 8i3 Of line relay til) before line relay Glfl has had suflcient time to restore. As soon as line relay 6E3 restores, resistor 609 is directly connected to the winding of cut-off relay 628 through the resting contact of armature 6. At armature 6H2, line relay 6H] completes the chain circuit to resistor 609 for all the other line circuits. The restoration of line relay 6L0 does not remove trigger .device 6 I8 from its position between the lower arm of armature 62B and the left-hand end of plate BIS, as armature I325 firmly holds trigger device 6I8 against the left-hand end of plate BIQ to retain left-hand vertical members SM, 562 and 663 in contact with conductors BI, 52 and I53 of trunk I.

Digressing for the moment from the description of the call from line I, an explanation will now be given of the method of automatically pie-assigning trunks to successive calls initiated at local stations of Figure 6. In the foregoing description it was stated that vertical bar 635 is associated with trunk I, and vertical bar 644 with trunk It. Bar 634 is controlled by lever 6 32, and bar 644 by lever 642. Lever $32 is controlled by cam 63L and lever .642 by cam MI. The cams are mounted on a common shaft 646 which is operative by electromagnet 630 through the medium of armature pawl I339. Lever 632 is pivoted at 633 and, consequently, when the lefthand end of lever 632 permitted bar 534 to drop by gravity to its lower position, the right-hand end of lever 632 closed contact 635 and opened contact 636. The seizing of the connector (not shown) associated with trunk I by line i caused ground potential to be extended to conductor c3 of trunk I in the manner previously described, and contact 635, therefore completes a multiple circuit to relay GIS and electromagnet G36, causing both relay (H5 and electromagnet see to operate. At armature GIG, relay 6I5 opens the multiple operating circuit for the cut-off relays of Figure e thereby to prevent the operation of any cut-01f relay of Figure 6 should another outgoing call be initiated at this time.

The operation of electromagnet 536 causes armature pawl 639 to advance shaft 546 one trunk step in a clockwise direction. Cam 63L therefore, leaves the right-hand end of lever 632, and the tensioned springs associated with contacts 635 and 635 cause lever 632 to raise bar 534 to the upper, or normal, position, contact 635 to open, and contact 636 to close. The opening of contact 635 opens the circuit to relay BIS and electromagnet $30. Electromagnet 530 restores immediately but relay 6I5 is of the slow-to-release type. Pawl 63? retains shaft 658 in the advanced position. Contact 636 has no function at this time. The raising of bar 634 has no effect on the established connection of line I with trunk I as cut-off relay G20 continues to hold plate BIB to the right thereby maintaining left-hand vertical members 56L E62 and 663 in firm contact with conductors GI, 62 and :33 of trunk I. The raising of bar 634, however, causes left-hand Vertical members SH, 672 and 613 to be returned to their original, or normal, positions in which positions the lower ends of these vertical members are above the horizontal plane of the top ends of the left-hand vertical arms of plate 651 and, therefore, no subsequent movement of plate 65"! to the right can cause the extension of line 56 to conductors 6|, 62 and 63 of occupied trunk I.

As the operation of armature pawl 639 stepped cam 63I away from lever 632, it also caused cam GM to approach and operate the right-hand end of lever 642 associated with trunk I0, thereby causing contact 645 to be closed. Assuming now that trunk I0 is in the idle position, then the lefthand end of lever 642 causes bar 644 to drop by gravity to its lower position, thereby pre-assigning trunk ID in a manner similar to that previously described in connection with the pro-assignment of trunk I. If, however, trunk I0 is occupied at the time contact 545 is closed, the multiple circuit to relay 6I5 and electromagnet will be completed, causing electromagnet sec to operate and retaining relay BIS in the operated position. Relay 6I5 is slow to release and, therefore, did not restore when its circuit was opened at contact 535 before its circuit is completed at contact 645. The function of relay EH5 is to maintain the multiple operating circuit to the cut-off relays of Figure 6 open while an idle trunk is being found and pro-assigned, in order that no calling line will be extended to an occupied trunk.

The re-operation of electromagnet 539 due to trunk iii being found in the busy condition causes armature pawl 639 to advance shaft 6 38 another trunk step which in the normal event would select trunk 9 (not shown in detail). Occupied trunk IQ is thus by-passed and contact 845 opened. If trunk 9 is in the idle position, then there will be no ground potential to complete the multiple circuit to electromagnet 630 and relay EH5, and trunk 9 is then pro-assigned in readiness for the next outgoing call on a line circuit of Figure 6. In the manner just described occupied trunks are by-passed and trunks in the idle position are pie-assigned.

Returning now to the connection of line I with the connector (not shown) associated with trunk I, as previously stated the ground on trunk conductor 63 from the connector (not shown) is extended through the left-hand vertical member 653 to the winding of cut-off relay 626 and to the C terminal of the connector bank terminals of line I. The ground on the winding of cut-off relay 628 causes cut-01f relay 520 to maintain the connection of line I with trunk I as long as the direct-current loop of line A remains intact. The ground to the C terminal of the connector terminals of line I guards line I from intrusion by other calls.

Assuming further that line I desires a connection with line then line I controls the connector (not shown) associated with trunk I in a well-known manner to cause the connector to connect with the bank terminals of line 56. The connector tests the 0 bank terminal of line 50 for a possible busy condition and finding line 50 in the idle position then connects ground potential to the winding of cut-off relay 550 by way of conductors fill, 673, SM, winding of cut-off relay 658, resting contact of armatures 628, conductor 6E5, resistor 6% to battery. Cut-off relay 65G operates over the circuit just traced and, at armatures BBI and 652, clears line 59 of attachments. Since armature 553 is shunted by armature Bil", the chain circuit through this line circuit is not opened at this time. The operation of cut-off relay 656 also causes armature 656 to operate but armature S56 cannot cause a movement of plate to the right because the lower arm of armature 656 just reaches the left-hand end of plate 557. The connector (not shown) of trunk I now automatically signals line 56 in a well-known manner, and when line 50 answers the call the signalling circuit is disconnected and a transmission circuit is established between lines I and 59 in a well-known manner.

Upon the termination of the conversation and the opening of the direct-current loop of line I, the connector (not shown) of trunk I is restored to normal in a well-known manner, thereby causing the removal of ground potential from conductors 603 and 614. The removal of ground potential from conductor 683 causes cut-off relay 62c to restore and reconnect line relay GIG across 627. The restoring of plate 659 causes the disconnection of left-hand vertical members 56!, 662 and 653 from conductors til, 62 and 63 of trunk I, and the disconnected left-hand vertical members SH, 652 and 563 are then restored to their original, or normal, positions in the manner described in the previously mentioned application in order that their lower ends may be raised above the horizontal plane of the top ends of the left-hand vertical arms of plate M9. The removal of ground potential from conductor M causes cut-off relay 659 to restore and reconnect line relay 640 across the conductors of line 5'3 at armatures 55! and 552. Trunk I is now in the idle position.

The call from line I (Figure 6) just described was extended over the individual trunk (trunk i) of the trunks accessible to lines I5l. Additional outgoing calls from this group of lines will be extended over the common trunks in rotation as long as trunk I remains occupied. However, in order to obtain the maximum benefit of graded trunking, it is essential to route originating traffic to trunk l whenever trunk I becomes idle even though a common trunk was pre-assigned in response to trunk i becoming occupied and, therefore, means are included in Figure 6 to disable the pre-assignment of the common trunk and cause trunk I to be preassigned immediately trunk 5 becomes idle. The manner in which trunk I is again pre-assigned is described in the following paragraph.

During the period trunk I is occupied, relay 580 is held operated by the ground potential on trunk conductor 63, and as soon as trunk I becomes idle the ground potential is removed from conductor 63 thereby causing relay E85 to restore. At armature 58L relay $86 completes a multiple circuit to relay M5 and ole"- tromagnet 639 from ground, armature 68!, contact 536 (closed when trunk I is in the idle position), interrupter armature 638, winding of relay 5I5 to battery, and from ground, armature 68L contact 636, interrupter armature 38, winding of electromagnet 635! to battery causing both relay M5 and electromagnet 530 to operate. At armature BIS, relay ilfi opens the multiple operating circuit for the cut-ofi relays of Figure 6 thereby to prevent the extension of a possible outgoing call to a trunk while trunk I is being yore-assigned. The operation of electromagnet 639 causes armature pawl 639 to advance shaft 6 55 one trunk step thereby causing the return of the previously pre-assigned common trunk (which will be assumed to be trunk It) to the normal idle position.

The operation of electromagnet 635 also causes interrupter armature 638 to open the multiple circuit to the windings or" electromagnet E30 and relay H5. Electromagnet etc restores but relay {H5 remains operated due to its slow-torelease nature. Pawl 637 retains shaft 666 in the advanced position. The restoration of interrupter armature 638 completes the multiple operating circuit to electromagnet 63d and relay 655, causing electromagnet 639 to re-operate and relay BIEi to remain operated. The re-operation of electromagnet see causes armature pawl 639 to advance shaft 64!? another trunk step and also causes interrupter armature 638 to again open the multiple operating circuit to the windings of electromagnet 630 and relay ISI5. Electromagnet I539 accordingly restores and again causes the completion of the multiple operating circuit at restored interrupter armature 638. This alternate action of the operation and restoration of electromagnet 63!! causing shaft 846 to be advanced one trunk step at a time continues until cam 63I reaches and raises the right-hand end of lever 632. The raising of the right-hand end of lever 632 causes the opening of contact 636 which in turn opens the multiple operating circuit to electromagnet G36 and relay M5, thereby preventing further advancing of shaft 646 and causing the re-espre-assignment of trunk I in the manner al-- ready described.

The operation of the lines and trunks shown:

in Figure '7 is the same as that just described. for the lines and trunks of Figure 6 with the general exceptions that trunk H is the individual trunk instead of trunk I and that the lines; are numbered EI and I60 instead of I and 50; It is, therefore, considered unnecessary to describe the operation of Figure 7.

Having described the invention, what is considered new and is desired to have protected by Letters Patent is pointed out in the following claims.

What is claimed is:

1. In a telephone system, lines having. line and cut-oif relays, said lines adapted for initiating outgoing calls simultaneously; said line and cutoil relays each having a normally closed contact, an incomplete chain circuit connected through said contacts of said cut-off relays for controlling the operation of said cut-off relays, said contacts of said line relays shunting said contacts of said cut-off relays thereby rendering said contacts of said cut-off relays normally ineiiective, means responsive to the initiation of an outgoing call on one of said lines for causing the line relay of said one line to operate and open its said contact thereby to remove said shunt from said contact of the cut-off relay of said one line and thus cause said contact of said one cut-off relay to become efiective, said operation of said one line relay completing said incomplete chain circuit through said one cut-oil relay thereby to cause the operation of said one cut-oiT relay, said operation of said one cut-off relay causing the opening of said completed chain circuit thereby to prevent the operation of any of said other cut-off relays should one or more additional outgoing calls be initiated at this time.

2. The telephone system as claimed in claim 1 and including means independent of said opened chain circuit for causing the operation of any one of said other cut-off relays when an incoming call is received for the line associated with said last cut-off relay.

3. In a telephone system, a plurality of lines, three relays individual to one of said lines, one of said relays connected to said one line, a trunk, connecting means individual to each of said lines, means responsive to the initiation of a call over said one line for operating said one relay, means controlled by said one operated relay for operating a second one of said relays, means for retaining said second relay in the operated position independent oisaid means controlled by said one operated relay, responsive to said operation of said second relay for operating said connecting means individual to said one line to connect said one line with said trunk, and means controlled by said operated second relay for causing the operation of third one of said relays to disable said means controlled by said one operated relay.

4. The telephone system as claimed in claim 3 together with a circuit controlled by said one operated relay to lock said operated third relay in the operated position, contacts on said operated second relay efiective to disconnect said one operated relay from said line thereby to cause the restoration of said one operated relay,

contacts on said one restored relay efiective to cause the restoration of said operated third relay.

5. In a telephone system, a plurality of lines, a line relay and a cut-off relay individual to one of said lines, a plurality of trunks, means for selecting an idle one of said trunks, connecting means, conditioning means, a source of power, means responsive to the initiation of a call over said one line for causing said line relay to operate, means responsive to said operation of said,

line relay for interposing said conditioning means between said cut-oil relay and said connecting means to condition said cut-off relay preparatory to causing the operation of said connecting means, said operation of said line relay extending said source to said conditioned cut-off relay to cause the operation of said conditioned cutoff relay, and means responsive to said operation of said conditioned cut-off relay for operating said connecting means to connect said one line with said one selected idle trunk.

6. In a telephone system as claimed in claim 5 wherein said last mentioned means also retains said interposed conditioning means independent of said interposing means controlled by said operated line relay, and wherein contacts on said operated cut-off relay operated to disable said operated line relay.

'7. In a telephone system, a plurality of lines, a line relay and a cut-off relay individual to one of said lines, a plurality of trunks, means common to said trunks for causing the interconnection of preselected ones or" said trunl s and said one line, means for preselecting an idle one of said trunks, means responsive to the initiation of a call over said one line for operating said line relay, means responsive to said operation of said line relay for preparing said cut-oif relay to operate said common connecting means, means responsive to said operation of said line relay for seizing said one pre-selected trunk, means responsive to said seizure of said one preselected trunk for causing said prepared cut-off relay to operate said common connecting means, and

means responsive to said operation of said com-- mon connecting means for interconnecting said one seized preselected trunk and said one line.

8. In a telephone system, a plurality of lines each having a line relay and a cut-off relay, said lines adapted for initiating calls simultaneously, said line relays having means in common for preventing any two of said line relays operating at one time should calls be initiated over the related lines simultaneously, a plurality of trunks, connecting means individual to each of said cut-oii relays for causing the interconnection of preselected idle ones of sai dtrunks and the related lines of said cut-ofi relays, means for preselecting an idle one of said trunks, means including said means in common for causing the operation of the line relay of one of said lines in response to the initiation of a call over said one line, means responsive to said operation of said one line relay for disabling said means in common to prevent any of said other line relays operating at this time, means responsive to said operation of said one line relay for preparing the cut-off relay of said one line to operate its individual connecting means, means responsive to said operation of said one line relay for seizing said one preselected trunk, means responsive to said seizure of said one preselected trunk for causing said one prepared cut-oif relay of said one line to operate the connecting means individual to said one prepared cut-off relay, means responsive to said operation of said connecting means individual to said one operated cut-ofi relay for connecting said seized preselected trunk and said one line together, contacts on said one operated cut-off relay operated to disable said one operated line relay, contacts on responsive said one disabled line relay operated to re-establish said means in common.

9. In a telephone system, lines having line and cut-off relays, said lines adapted for initiating outgoing calls simultaneously said line and cutofi relays each having a normally closed contact, an incomplete chain circuit connected through said contacts of said cut-off relays, said contacts of said line relays shunting said contacts of said cut-off relays, means responsive to the simultaneous initiation of outgoing calls on two of saidl lines for causing the line relays of said two lines to operate and respectively open their said contacts, thereby to respectively remove said shunts from said contacts of the cut-off relays of said two lines, the operated line relay of one of said lines having other contacts operated to complete said incomplete chain circuit through the cut-oii relay of said one line to cause the operation of said cut-off relay of said one line, said operation of said cut-off relay of said one line opening its said contact to disable said chain circuit thereby to prevent the operation of the cut-oil relay of said other line at this time, means independent of said chain circuit locking said operated cut-off relay of said one line in the operated position, of said operated cut-off relay of said one line having other contacts operated to cause said operated line relay of said one line to restore, said restoration of said operated line relay of said one line closing its opened contact to partly re-establish said disabled chain circuit, the operated line relay of said other line having other contacts operated to complete said partly re-established chain circuit through the cut-off relay of said other line to cause the operation of said cut-01f relay of said other line.

10. In a telephone system, lines each having a line relay, commons means controllable by any of said line relays for preventing the operation of more than one of said line relays at one time when calls are initiated over more than one of said lines simultaneously, means including said common means for causing the operation of the line relay of a certain one of said lines responsive to the initiation of a call over said one certain line, means responsive to said operation of said line relay of said one certain line for disabling said common means to prevent any of said other line relays operating at this time, means for causing said one operated line relay to restore, contacts on said one restored relay operated to re-establish said disabled common means, means including said re-established common means for causing the operation of another one of said line relays in response to the initiation of a call over the line related to said other line relay, means responsive to said operation of said other line relay for disabling said re-established common means, and means for causing said one restored line relay to re-operate independent of said last disabled common means.

11. In an automatic telephone system, lines each having an A relay, a B relay, and a C relay, and means for transmitting pulses common means controllable by any of said A relays for preventing the simultaneous operation of more than one of said A relays when calls are initiated over more than one of said lines at the same time, means including said common means for operating the A relay of one of said lines responsive to the initiation of a call over said one line, means responsive to said operation of said one A relay for disabling said common means to prevent any of said other A relays operating at this time, means controlled by said one operated A relay for causing the B relay of said one line to operate, means controlled by said one operated B relay for operating the C relay of said one line, contacts on said one operated B relay operated to cause said one operated A relay to restore, means for re-establishing said disabled common means controlled by said one restored A relay, means including said re-established common means for operating the A relay of another of said lines responsive to the initiation of a call over said other line, means for disabling said reestablished common means responsive to said operation of said A relay of said other line, means controlled by said one operated C relay for partly preparing an operating circuit independent of said disabled re-established common means for said one restored A relay, means effective after the expiration of a predetermined time interval and before a pulse is received over said one line to cause the restoration of said one operated B relay, means controlled by said one restored B relay for completing said partly prepared operating circuit of said one restored A relay to cause the re-operation of said one restored A relay, and means controlled by said one reoperated A relay for locking said one operated C relay in the operated position to maintain said one re-operated A relay in the operated position.

12. The automatic telephone system as claimed in claim 11 together with means responsive to the abandonment of said call initiated over said one line for causing the restoration of said one reoperated A relay, and means controlled by said one re-operated A relay for disabling said one locked C relay.

13. In a telephone system, two groups of lines, trunks, one of said trunks accessible to the lines of only one of said groups, others of said trunks accessible in common to the lines of both said groups, means for pre-assigning said one trunk in preparation for seizure by any one of the lines of only said one group, means responsive to the initiation of a call over one of the lines of said one group for seizing said one pre-assigned trunk, means responsive to said seizure of said one preassigned trunk for connecting said one line of said one group with said one seized trunk, said first mentioned means responsive to said connection of said one line of said one group pre-assigning one of said common trunks in preparation for seizure by another of the lines of said one group or by one of the lines of said other group, means responsive to the abandomnent of said connection of said one line of said one group with said one seized trunk for releasing said one seized trunk, means responsive to said releasing of said one seized trunk for disabling said pre-assignment of said one common trunk, said first mentioned means responsive to said disablement of said pre-assignment of said one common trunk pre-assigning said one released trunk in preparation for seizure by any one of the lines of only said one group.

14. In a telephone system, lines having, line relays and cut-01f relays, two trunks, means for preassigning one of said trunks, connecting means individual to each of said cut-oil relays, means responsive to the initiation of a call over one of said lines for operating the line relay of said one line, means responsive to said operation of said one line relay for preparing the cut-oil relay of said one line to operate the connecting means individual to said one cut-off relay, means controlled by said one operated line relay for causing said one prepared cut-ofi relay to operate said one connecting means, said operation of said one connecting means connecting said one pre-assigned trunk and said one line together, said first mentioned means responsive to said connection of said one line pre-assigning said other trunk in preparation for seizure by another of said lines, means responsive to said one line terminating said connection of said one line for releasing said one connected trunk, means responsive to said releasing of said one connected trunk for disabling said preassignment of said other trunk, said first mentioned means responsive to said disablement of said pre-assignment of said other trunk preassigningsaid one released trunk in preparation for seizure by any one of said lines.

15. In a telephone system, a line having a line relay and a cut-off relay, said line relay connected to said line, a trunk, connectin means, means responsive to the initiation of a call over said line for operating said line relay, means responsive to said operation of said line relay for preparing said cut-ofi relay to operate said connecting means, means responsive to said operation of said line relay for seizin said trunk, means responsive to said seizure of said trunk for causing said prepared cut-off relay to operate, means controlled by said operations of said line relay and said cut-0E relay for temporarily holding said operated cut-ofi rela in the operated position, means responsive to said operation of said cut-oil relay for operating said connecting means, means responsive to said operation of said connecting means for connecting said trunk and said line together, means controlled by said connection of said seized trunk and said line for locking said operated cut-off relay in the operated position independent of control by said holding means, means controlled by said operated cut-01f relay for disconnecting said operated line relay from said line to cause the restoration of said operated line relay, said contacts on said restored line relay operated to disable said holding means.

ROY W. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,484,771 Goodrum Feb. 26, 1924 1,540,419 Powell June 2, 1925 

